There are many circumstances where the cooling of CMOS logic circuits may degrade resulting in substantially higher operational junction temperatures. The temperature increase may be sufficient that the speed of the circuits and wiring reliably switch only if the clocks governing the switching speeds of these circuits are slowed.
There are numerous ways the temperature of specific logic components within a server may substantially increase in temperature; such as when air cooling and the ambient temperature rises dramatically as in the case of a failed air conditioning system; such as when the thermal conductive path between the logic devices and convective surfaces experience an increase in thermal resistance due to degradation of the thermal properties of the conductive path or improper assembly; such as when the quantity of airflow providing the air cooling drops dramatically due to debris clogging the fins of a heat sink or a fan failure; and such as computer applications that have very intensive switching factors resulting in much higher power generation while running that operation. Lastly, in which this invention is primarily concerned, this temperature change occurs when the primary means of cooling the logic circuits provides substantially lower junction temperatures than the secondary or backup means of cooling can provide and a switch between primary and secondary cooling modes occurs. A switch to the secondary means happens when the primary means of cooling using either refrigeration or water cooling is inadequate and the backup mode of air cooling is an attempt for redundant cooling.
The performance and reliability of high power CMOS circuits is improved using liquid cooling means such as refrigeration or water rather than air cooling. Non-redundant liquid cooling may help the circuits but the cooling system failure rate is too high for most electronics applications (e.g., servers) without a cooling backup.
Furthermore, the aggregated componentry of such configurations may occupy considerable volumes within their respective systems such that redundant liquid cooling is not possible. Because space is at a premium in most electronics applications, particularly as the size of the systems are reduced to keep pace with technological trends, cooling systems may be likewise reduced in size. In addition, higher end modules having increased density of electronic circuitry require redundant or backup cooling means in the event that the primary refrigeration cooling unit fails, while limiting the space needed to employ such a redundant or secondary cooling means.
Current methods of handling a significant degradation in observed logic temperatures for a single large change in cycle time includes cutting the clock speed in half. This method lowers the power being generated by the logic device sufficiently such that damage concerns due to high temperatures are eliminated. This approach is essentially simple thermal protection to prevent damage to the logic device. The prior art discloses essentially a high speed or low speed approach based on thermal protection concerns, and does not focus on operating the clock speeds at their optimal performance point all the way until thermal shutdown occurs for hardware protection.